Nitride compound semiconductor element and method for manufacturing same

ABSTRACT

The present invention is directed to a production method for a nitride compound semiconductor element including a substrate and a multilayer structure  40  supported by an upper face of the substrate. First, a wafer  1  to be split into individual substrates is provided. A plurality of semiconductor layers composing the multilayer structure  40  are grown on the wafer  1 . By cleaving the wafer  1  and the semiconductor layers, a cleavage plane in the multilayer structure  40  is formed. In the present invention, a plurality of voids are arranged at positions in the multilayer structure at which a cleavage plane is to be formed. Thus, cleavage can be performed with a good yield.

TECHNICAL FIELD

The present invention relates to a nitride compound semiconductorelement and a production method therefor.

BACKGROUND ART

A band gap of a nitride compound semiconductor whose composition isexpressed by the general formula In_(x)Ga_(y)Al_(z)N (where x+y+z=1,0≦x≦1, 0≦y≦1, 0≦z≦1) may have a size corresponding to blue light orultraviolet light through adjustment of the mole fraction of eachelement. Therefore, there have been vigorous research activitiesdirected to light-emitting devices, e.g., semiconductor lasers, thatcomprise a nitride compound semiconductor as an active layer.

FIG. 1 shows the crystal structure of a nitride compound semiconductor.As shown in FIG. 1, a nitride compound semiconductor has a crystalstructure of a hexagonal-system. Therefore, when fabricating asemiconductor laser which is constructed so that its upper face(principal face) is the (0001) plane and its resonator end faces are theM-plane (1-100), cleavage is likely to occur not along an A-plane whichis perpendicular to these planes, but along a crystal plane which istilted by 30° from the A-plane. As a result, there is a problem in that,not only when performing cleavage along the A-plane, but also whenforming cleavage along the M-planes (1-100) to form the resonator endfaces, miscleavage (end-face cracks) is likely to occur in a directionwhich is tilted by 60° from the M-plane (1-100).

Due to this problem, it has conventionally been very difficult tofabricate a nitride compound semiconductor element having smoothresonator end faces.

A sapphire substrate, which has conventionally been widely used as asubstrate for nitride compound semiconductor elements, is not capablecleaving. Therefore, when forming a semiconductor laser having asapphire substrate, it has been practiced to perform scribing along theM-plane from the side of a nitride compound semiconductor layer that isgrown on a sapphire substrate to thus form a scratch in the nitridecompound semiconductor layer, this being an attempt to facilitate theformation of a cleavage plane.

Patent Document 1 discloses a method which involves performing an edgescribing for a nitride compound semiconductor layer, and thereafterperforming a cleavage through breaking.

Similarly in the case of cleaving a semiconductor laser comprising a GaNsubstrate, which is being used in the recent years, it has beenpracticed to form scribing grooves along the M-plane from the side of anitride compound semiconductor layer that is grown on the GaN substrate,this being an attempt to facilitate cleavage. Patent Document 2discloses a method of, after linearly forming scribing grooves in anitride compound semiconductor layer, performing a cleavage throughbreaking.

-   [Patent Document 1] Japanese Laid-Open Patent Publication No.    2000-058972-   [Patent Document 2] Japanese Laid-Open Patent Publication No.    2003-17791

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, according to the aforementioned conventional technique, sincescratches are formed in the nitride compound semiconductor layer throughscribing or dicing, there is a problem in that “burrs”, “chipping”,“end-face cracks”, scribing dust, and the like are likely to occur, thusresulting in a reduced production yield. There is also a problem inthat, since the active layer is likely to suffer from strain and crystaldefects, scratches and ruggednesses may occur in a resonator end face(light-outgoing surface), thus deteriorating the optical characteristicsand reliability.

The present invention has been made in order to solve the aforementionedproblems, and a main objective thereof is to provide a nitride compoundsemiconductor element which allows cleavage to be performed with a goodyield, and a production method therefore.

Means for Solving the Problems

A production method for a nitride compound semiconductor elementaccording to the present invention is a production method for a nitridecompound semiconductor element including a substrate having an upperface and a lower face and a multilayer structure supported by the upperface of the substrate, the production method comprising: a step ofproviding a wafer to be split into the substrate; a step of growing aplurality of semiconductor layers composing the multilayer structure onthe wafer; and a step of performing cleavage of the wafer and themultilayer structure to form a cleavage plane, further comprising a stepof arranging a plurality of voids at positions where the cleavage planeis to be formed.

In a preferred embodiment, a cross section of each void in a plane whichis parallel to the wafer is sized and shaped so as to be accommodatedwithin a rectangular region of 10 μm×10 μm.

In a preferred embodiment, the step of arranging the plurality of voidscomprises a step of pressing a tip of a needle piece against an upperface of the multilayer structure to form depressions on the multilayerstructure, the depressions functioning as the voids.

In a preferred embodiment, an angle formed between a direction which isperpendicular to the wafer and a pressing direction when the tip of theneedle piece is abutted against the upper face of the multilayerstructure is set to 5° or more.

In a preferred embodiment, the nitride compound semiconductor element isa semiconductor laser having as a resonator end face a cleavage planewhich is parallel to a plane containing the pressing direction.

A nitride compound semiconductor element according to the presentinvention is a nitride compound semiconductor element comprising asubstrate having an upper face and a lower face and a multilayerstructure supported by the upper face of the substrate, such that thesubstrate and the multilayer structure have at least two cleavageplanes, wherein, the multilayer structure includes at least one voidwhich is in contact with either of the two cleavage planes.

In a preferred embodiment, the upper face of the substrate has arectangular shape, and the void is located at at least one of fourcorners of the upper face of the substrate.

In a preferred embodiment, a cross section of the void in a plane whichis parallel to the upper face of the substrate is sized and shaped so asto be accommodated within a rectangular region of 10 μm×10 μm.

In a preferred embodiment, the multilayer structure has a laserresonator structure including: an n-type nitride compound semiconductorlayer and a p-type nitride compound semiconductor layer; and an activelayer interposed between the n-type nitride compound semiconductor layerand the p-type nitride compound semiconductor layer, at least a portionof the cleavage planes functioning as a resonator end face.

In a preferred embodiment, an interval between a bottom of the void andthe substrate is smaller than an interval between the active layer andthe substrate.

In a preferred embodiment, a trench is formed between a laser opticalwaveguide portion and the void in the multilayer structure.

In a preferred embodiment, an interval between the bottom of the trenchand the substrate is smaller than an interval between the active layerand the substrate.

In a preferred embodiment, the substrate is a nitride compoundsemiconductor.

A preferred embodiment comprises a rear electrode formed on the lowerface of the substrate, wherein, the rear electrode has a planar patternwhich allows the void to be visually recognized through the lower faceof the substrate.

Effects of the Invention

According to the present invention, the arrangement of voids contributesto an accurate positioning of cleavage planes, and therefore theproduction yield of a nitride compound semiconductor, which is difficultto be cleaved, is greatly improved. As compared to scribing grooves, thevoids have a sufficiently small size along the cleavage plane direction.Therefore, positioning accuracy of the cleavage planes can be enhancedwith respect to both primary cleavage and secondary cleavage. Moreover,since dot-like voids are arranged in a discrete manner, it becomespossible to suppress deviation of cleavage planes as compared to thecase of linear scribing grooves.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A perspective view showing the crystal structure of a nitridecompound semiconductor.

FIG. 2 A plan view showing the relationship between an arrangement ofvoids 3 and cleavage directions.

FIGS. 3 (a) and (b) are cross-sectional views showing steps of forming amultilayer structure on a wafer according to an embodiment of thepresent invention.

FIG. 4 A diagram showing an arrangement of voids 3 according toEmbodiment 1 of the present invention.

FIGS. 5 (a) and (b) are diagrams each schematically showing a method forforming the voids 3.

FIG. 6 (a) is a diagram showing a state before cleavage steps; and (b)is a diagram showing one of individual chips after cleavage.

FIG. 7 (a) is a plan view showing a manner of primary cleavage accordingto an embodiment of the present invention; and (b) is a plan viewshowing a manner of primary cleavage in Comparative Example.

FIG. 8 (a) is a plan view showing a manner of secondary cleavageaccording to an embodiment of the present invention; and (b) is a planview showing a manner of secondary cleavage in Comparative Example.

FIG. 9 (a) to (c) are plan views showing rear electrode patternsaccording to preferable embodiments of the present invention.

FIG. 10 (a) is an upper face showing another embodiment of thesemiconductor element according to the present invention; and (b) is across-sectional view thereof.

FIG. 11 (a) is an upper plan view showing still another embodiment ofthe semiconductor element according to the present invention; and (b) isa cross-sectional view thereof.

FIG. 12 (a) is an upper plan view showing still another embodiment ofthe semiconductor element according to the present invention; and (b) isa cross-sectional view thereof.

FIG. 13 (a) is an upper plan view showing an arrangement of voids 300according to Embodiment 2 of the present invention; (b) is a plan viewshowing a shape of the voids 300; and (c) is a plan view showing anothershape of the voids 300.

FIG. 14 (a) is an upper plan view showing another arrangement of thevoids 300 according to Embodiment 2 of the present invention; and (b) isa plan view showing shapes of voids 300 a, 300 b, and 300 c.

FIG. 15 (a) is an upper plan view showing another arrangement of thevoids 300 according to Embodiment 2 of the present invention; (b) is aplan view showing a structural unit based on voids 300 a; and (c) is aplan view showing a void 300 c which is provided at a position near anedge scribing.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 wafer-   10 n-type GaN layer-   11 cladding layer of n-type Al_(0.04)Ga_(0.96)N-   12 first optical guide layer of n-type GaN-   13 multi-quantum well active layer-   14 capping layer of p-type Al_(0.15)Ga_(0.85)N-   15 second optical guide layer of p-type GaN-   16 p-type cladding layer of p-type Al_(0.05)Ga_(0.95)N-   17 p-type contact layer of p-type GaN-   20 electrode layer (rear electrode)-   30 linear void (scribing groove)-   35 trench-   45 needle piece for forming voids-   300 void

BEST MODE FOR CARRYING OUT THE INVENTION

A nitride compound semiconductor element according to the presentinvention includes a substrate having an upper face and a lower face,and a multilayer structure which is supported by the upper face of thesubstrate, such that the substrate and the multilayer structure have atleast two cleavage planes. In the present invention, in order tofacilitate “cleavage” of a crystal during its production steps, aplurality of “voids” are arranged on the upper face of a multilayerstructure which is provided on a wafer to become a substrate. Sincecleavage occurs along the arrangement of voids, (at least a portion of)a void(s) exists in most of the semiconductor elements that are finallyobtained.

Voids are arranged in a discrete manner in the wafer plane, and have asize which is sufficiently small relative to an interval between twocleavage planes of parallel relationship. In a plane which is parallelto the wafer plane, a void is preferably sized so as to be contained ina rectangular region of 10 μm (vertical)×10 μm (horizontal). Byperforming cleavage by utilizing an arrangement of such small voids,various effects which will be specifically described later are enabled.

Hereinafter, with reference to the drawings, main features of thenitride compound semiconductor element according to the presentinvention will be described. The nitride compound semiconductor elementaccording to the present invention is preferably a semiconductor laserwhose cleavage planes are utilized as resonator end faces, but may beany other light-emitting device, e.g., an LED (Light Emitting Diode), ora transistor. Although a semiconductor element other than asemiconductor laser does not utilize its cleavage planes as resonatorend faces, the ability to separate a hard nitride compound into chipswith a good yield through cleavage produces advantages such asfacilitated production.

First, FIG. 2 is referred to. FIG. 2 is an upper plan view of a waferhaving a multilayer structure formed on an upper face thereof.

In the example shown in FIG. 2, dot-like voids 3 are provided at pointswhere lines 25 intersect lines 26. Herein, after a primary cleavage isperformed along the lines 25, a secondary cleavage is performed alongthe lines 26. Each region surrounded by two adjoining lines 25 and twoadjoining lines 26 constitutes an individual semiconductor laser (chip).

The voids 3 can easily be formed by pressing the tip of a needle pieceagainst the upper face of a multilayer structure. For example, the tipof a needle piece which is composed of diamond may be processed so as tohave a diameter of about several μm, and, via pressing, minutedepressions which lie discretely in a two-dimensional manner can beformed on the upper face of a multilayer structure. Rather than being“scribing grooves” which extend longitudinally in a direction that isparallel to the wafer plane, these depressions are shaped so as torelatively approximate “points”, thus being able to appropriately guidenot only primary cleavage along the lines 25 but also guide secondarycleavage along the lines 26.

Cleavage can be begun by, after scribing scratches are formed near awafer end face at positions for forming cleavage planes, applying aforce from the wafer rear face to the portions where the scribingscratches are formed, by using a breaking apparatus. The three thicksolid lines shown in FIG. 2 show scribing scratches which are providedfor the sake of primary cleavage.

Hereinafter, preferable embodiments of the present invention will bedescribed.

Embodiment 1

First, with reference to FIGS. 3( a) and 3(b), processes of stackingsemiconductor layers on an upper face of a wafer 1 will be described.FIGS. 3( a) and 3(b) are partial cross-sectional views. In actuality,the illustrated portion is merely a part of a wafer which is sized witha diameter of about 50 mm.

As shown in FIG. 3( a), a GaN wafer 1 whose upper face is the (0001)plane is provided. Note that the cross section of the GaN wafer 1 thatis shown in FIGS. 3( a) and 3(b) is the (1-100) plane, which will beexposed through primary cleavage. The <11-20> direction lies in theplane of the figure, and is parallel to the upper face (0001) of the GaNwafer 1.

Next, as shown in FIG. 3( b), a multilayer structure 40 of a nitridecompound semiconductor is formed on the GaN wafer 1. In the presentembodiment, a metal-organic vapor phase epitaxy (MOVPE) technique isused to grow layers of nitride compound semiconductor expressed asIn_(x)Ga_(y)Al_(z)N (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1). Specifically,the multilayer structure 40 is formed as described below.

First, the GaN wafer 1 is retained on a susceptor in a reactor of MOVPEequipment. Then, the reactor is heated to about 1000° C., and sourcegases, i.e., trimethylgallium (TMG) and ammonia (NH₃) gas, and a carriergas of hydrogen and nitrogen are simultaneously supplied, and silane(SiH₄) gas is supplied as an n-type dopant, thus allowing an n-type GaNlayer 10 having a thickness of about 1 μm and an Si impurityconcentration of about 5×10¹⁷ cm⁻³ to grow.

Thereafter, while also supplying trimethylaluminum (TMA), an n-typecladding layer 11 composed of n-type Al_(0.04)Ga_(0.96)N with athickness of about 1.8 μm and an Si impurity concentration of about5×10¹⁷ cm⁻³ is grown. Then, after growing a first optical guide layer 12composed of n-type GaN with a thickness of about 150 nm and an Siimpurity concentration of about 5×10¹⁷ cm⁻³, the temperature is loweredto about 800° C., the carrier gas is changed to nitrogen only, andtrimethylindium (TMI) and TMG are supplied, thus growing quantum wells(three layers) composed of In_(0.10)Ga_(0.90)N with a film thickness ofabout 3 nm and a multi-quantum well active layer 13 composed ofIn_(0.02)Ga_(0.98)N barrier layers (two layers) with a film thickness ofabout 9 nm.

The temperature within the reactor is again elevated to about 1000° C.,hydrogen is mixed to the carrier gas, and while supplying a p-typedopant of biscyclopentadienylmagnesium (Cp₂Mg) gas, a capping layer 14composed of p-type Al_(0.15)Ga_(0.85)N with a film thickness of about 10nm and an Mg impurity concentration of about 1×10¹⁹ cm⁻³ is grown.

Next, a second optical guide layer 15 composed of p-type GaN with athickness of about 120 nm and an Mg impurity concentration of about1×10¹⁹ cm⁻³ is grown. Thereafter, a p-type cladding layer 16 composed ofp-type Al_(0.05)Ga_(0.95)N with a thickness of about 0.5 μm and animpurity concentration of about 1×10¹⁹ cm⁻³ is grown. Finally, a p-typecontact layer 17 composed of p-type GaN with a thickness of about 0.1 μmand an Mg impurity concentration of about 1×10²⁰ cm⁻³ is grown.

Note that, in carrying out the present invention, the specificconstruction of the multilayer structure 40 and the method for growingsemiconductor layers may be arbitrarily chosen, and the aforementionedconstruction and growth method are only exemplary.

After the multilayer structure 40 is formed, a step of forming striperidges for current confinement, a step of forming electrodes, a step ofpolishing the rear face of the wafer 1, and the like are performed,after which a step of forming the voids 3 is performed. Note that, inthe step of polishing the rear face of the wafer 1, the thickness of thewafer 1 is reduced to about 100 μm.

Hereinafter, with reference to FIG. 4, an exemplary arrangement of thevoids 3 and a method for forming the voids will be described. Forsimplicity, the detailed construction of the multilayer structure 40 isnot shown in FIG. 4. Moreover, the aforementioned ridge stripes,electrodes, and the like will be present on the upper face of an actualmultilayer structure 40, which is not smooth as shown in FIG. 4.

The voids 3 in the present embodiment are arranged in a discrete mannerin a matrix shape along the <11-20> direction and along <1-100>, and donot intersect optical waveguides 18 which are formed in the multilayerstructure 40. The distance between two adjoining voids 3 along the<11-20> direction is set to be substantially the same value as the sizealong the <11-20> direction (chip width) of the finally-obtained laserdevice. In the present embodiment, the size along the <11-20> directionof each laser device is about 200 μm, and therefore the arraying pitchof the voids 3 along the <11-20> direction is also set at 200 μm. On theother hand, the arraying pitch of the voids 3 along the <1-100>direction is set at a value which is equal to the resonator length ofeach laser device. In the present embodiment, the resonator length isabout 600 μm, and therefore the arraying pitch of the voids 3 along the<1-100> direction is also set at 600 μm. Note that the size of the laserdevice is not limited to the aforementioned values, but the arrangementinterval of the voids 3 may be set to any appropriate value inaccordance with the size of the laser device.

In a plane which is parallel to the upper face of the wafer 1, each void3 is set to a size of 10 μm×10 μm or less. In a cross section which isparallel to the upper face of the wafer 1, each void 3 typically has acircular shape (with a diameter of about 3 μm), but may also have anelliptic shape. In the case where the cross section shape is an ellipse,its size along the major axis direction may be set to e.g. about 5 to 6μm, and its size along the minor axis direction may be set to e.g. about2 to 3 μm. Note that the depth of each void 3 is about 2 to 7 μm. Thus,by arranging, along lines 25 and lines 26 shown in FIG. 4, the voids 3which are sufficiently small relative to the size of each laser device,it becomes possible to perform both of primary and secondary cleavagesat accurate positions.

Each line 25 shown in FIG. 4 is defined by a row of plural voids 3 whichare arranged along the <11-20> direction, and primary cleavage is totake place along these lines 25. On the other hand, secondary cleavageis to take place along the lines 26. Therefore, preferably, the voids 3are disposed at the intersections (lattice points) where the lines 25intersect the lines 26. However, it is not necessary to provide a void 3at every intersection where a line 25 intersects a line 26.

FIG. 5( a) and FIG. 5( b) are diagrams each schematically showing a stepof forming the voids 3. For simplicity, stripe ridges and electrodes areomitted from illustration in FIG. 5.

In the example shown in FIG. 5( a), a needle piece 45 is moved up anddown along a direction which is perpendicular to the upper face of thewafer 1, thus forming depressions (voids) on the multilayer structure 40in a discrete manner. The wafer 1 may be moved in synchronization withthe up-down motion of the needle piece 45, whereby minute depressions(voids) can be formed at the positions of the lattice points shown inFIG. 4. In a lower portion of FIG. 5( a), a planar shape of thedepressions (voids 3) to be formed is schematically shown. Forsimplicity, in the example shown in the lower portion of FIG. 5( a), thevoids 3 are illustrated as having an isotropic shape in a plane which isparallel to the surface of the wafer 1. However, by adjusting the crosssection shape of the tip of the needle piece 45, it becomes possible toform voids 3 with a variety of shapes. In order to guide cleavage alonga predetermined direction, it is preferable that each individual void 3has an anisotropic shape with a longitudinal axis extending along thecleavage direction.

In the example shown in FIG. 5( b), the needle piece 45 is tilted fromthe direction which is perpendicular to the upper face of the wafer 1.By introducing such a tilt, as shown in a lower portion of FIG. 5( b),depressions of a shape that is somewhat elongated along the <11-20>direction (which is the direction of primary cleavage) are formed. Inthe case where the tip of the needle piece 45 has a triangular pyramidshape, for example, performing the pressing maneuver in a tilted statesuch that a ridge line (edge) of the triangular pyramid is turned towardthe wafer 1 will allow depressions to be formed with an even smallerforce on the upper face of the multilayer structure 40. By obliquelypressing the needle piece 45, abrasive deterioration of the needle piececan be suppressed. Preferably, the angle formed between the pressingdirection and the direction which is perpendicular to the wafer is setto 5° or more, and is set in a range of 10° to 45°, for example.

Hereinafter, with reference to FIGS. 6( a) and (b), cleavage steps willbe described. FIG. 6( a) shows a state before the split, whereas FIG. 6(b) shows one of the individual split-chips.

After forming the voids 3 with the aforementioned method, a primarycleavage is performed along the lines 25 shown in FIG. 6( a). At thistime, a stress may be applied from the rear face of the wafer 1 by usingan apparatus which is not shown, whereby cleavage will progress along aplurality of voids 3 arranged along the lines 25 which are parallel tothe <11-20> direction. As a result, occurrence of miscleavage (end-facecracks) in the 60° direction is suppressed, so that laser bars havingsmooth resonator end faces of the M-plane, i.e., the (1-100) plane, arefabricated.

According to the present embodiment, the presence of the voids 3 makesit difficult for disruption of the laser bars due to the aforementionedcracks to occur. Thus, it is possible to make long laser bars, reducethe production cost as a result of improving the production efficiency,and improve the yield.

Next, after forming a dielectric protection film composed of niobiumoxide (Nb₂O₅) on one (outgoing side) of the resonator end faces of eachlaser bar obtained through the primary cleavage and a multilayereddielectric film composed of SiO_(x) and Nb₂O₅ on the other (reflectingside), a secondary cleavage is performed along the lines 26, wherebylaser chips (individual semiconductor lasers) are separated from eachlaser bar. Each semiconductor laser includes as its substrate a chipwhich has been split from the wafer 1.

After the cleavage steps are finished in this manner, via solder, eachsemiconductor laser is placed in such a manner that its n-side portionis in contact with the upper face of a submount which is composed ofaluminum nitride (AlN) or the like, and wiring is performed via wirebonding. At this time, by taking advantage of the voids 3 being inspecific positions of the laser device, the voids 3 can also exhibit afunction as positioning markers during the packaging step.

The laser device which has been produced by the above method has smoothresonator surfaces. At room temperature, continuous oscillation wasconfirmed at an operating current of 80 mA, with a threshold current of30 mA and an output power of 75 mW, and a lifespan of 1000 hours or morewas exhibited.

Although cleavage is also performed along the lines 26 in the aboveexample, the faces other than the resonator end faces do not need to becleavage planes. Therefore, cutting with laser, etc., may be performedalong the lines 26. However, since the voids 3 according to the presentinvention have a sufficiently small size along the <11-20> direction, anadvantage is provided in that secondary cleavage can be carried out witha good yield.

Although cleavage is occurring at positions traversing the voids 3 inthe example shown in FIG. 6( b), the cleavage planes do not always needto traverse the voids 3, but instead may be formed near the voids 3. Asshown in FIG. 6( b), when first order and secondary cleavages occur soas to traverse the voids 3, a portion(s) of a void(s) 3 will becontained at the four corners of each semiconductor laser chip that isfinally obtained. However, each individual semiconductor laser does notneed to contain portions of voids 3 in all of its four corners.Depending on the position of the cleavage plane, the number of (aportion or a whole of) voids 3 to be contained in each individualsemiconductor laser may fluctuate. In an extreme case, a givensemiconductor laser may finally contain no void 3. In such a case, asemiconductor laser adjoining that semiconductor laser will contain atleast one void 3.

The interior of the voids 3 may be filled also with materials other thanair. Although cleavage is possible even if the interior of the voids 3is filled with some material, cleavage will be facilitated in the casewhere it is not filled with a solid material.

Next, with reference to FIG. 7 and FIG. 8, the reason why voids aresuperior to linear voids (scribing grooves) will be described.

FIG. 7( a) is a plan view showing a manner of primary cleavage accordingto an embodiment of the present invention; and FIG. 7( b) is a plan viewshowing a manner of primary cleavage in Comparative Example. In theembodiment of the present invention, each void 3 is able to serve as apoint from which to begin cleavage, and therefore, even if an angle θ isdeviated during primary cleavage, the position of the cleavage planewill be corrected at each void 3 as the cleavage progresses(self-restoration of cleavage positions). As a result, the cleavageplane will not greatly deviate from its intended position. On the otherhand, in Comparative Example where scribing grooves of length exceeding40 μm are arranged, as shown in FIG. 7( b), once a cleavage plane beginsto deviate, the cleavage plane is likely to greatly deviate from theintended position because the scribing grooves 30 do no have thefunction of correcting the deviation.

FIG. 8( a) is a plan view showing a manner of secondary cleavageaccording to an embodiment of the present invention; and FIG. 8( b) is aplan view showing a manner of secondary cleavage in the ComparativeExample. In FIG. 8, cleavage planes are shown by broken lines. In thecase where secondary cleavage is performed along the <1-100> direction,the voids 3 in the present embodiment effectively exhibit a function ofpositioning the cleavage planes (improvement in the A-plane accuracy).This is because the voids 3 have a sufficiently small size along adirection which is perpendicular to the <1-100> direction. On the otherhand, in the Comparative Example, as shown in FIG. 8( b), scribinggrooves extend longitudinally along a direction which is perpendicularto the <1-100> direction, so that the function of defining the positionsof secondary cleavage planes cannot be fully exhibited, and the cleavageplanes are likely to greatly deviate from their intended positions.

As is clear from the foregoing, in order to allow the effect ofpositioning the cleavage planes to be fully exhibited regarding not onlyprimary cleavage (M-plane cleavage) but also secondary cleavage (A-planecleavage), it is preferable that the voids for inducing or guidingcleavage are in the shape of dots. Moreover, it is most preferable thata dot-like void is located at each of the intersections between lines 25and 26 shown in FIG. 6.

Hereinafter, a preferable method of forming electrodes for allowingcleavage to be performed appropriately will be described.

Since GaN transmits visible light, it is possible to visually recognizethe voids 3 through the rear face of the wafer 1 of GaN. Therefore, inthe case where an electrode layer is formed on the rear face of thewafer 1, it is preferable to pattern the electrode layer 20 into shapesas shown in FIGS. 9( a) to (c). In each of the examples shown in FIG. 9,aperture regions for allowing the voids 3 to be visually recognizedthrough the lower face (rear face) of the wafer 1 are formed in theelectrode layer 20. Note that the aperture regions in the electrodelayer 20 on the rear face of the wafer 1 should be as narrow as possibleat the ridge positions to become current injection paths, as shown inFIG. 9( c). The reason is as follows. When a current is injected at aridge position, there is a large heat generation near the active layerunder the ridge, and in the case of operation with a high output power,there is also a large local heat generation at the laser end faces.Therefore, by increasing the area of the underlying electrode layer 20,release of heat to the submount can be performed efficiently.

Next, with reference to FIG. 10 to FIG. 12, more preferable embodimentsof the semiconductor element according to the present invention will bedescribed.

In the semiconductor laser device shown in FIG. 10, the voids 3 areformed so as to be deeper than the position of the active layer 13. Atcleavage, “miscleavage (end-face cracks)” such as end face unevennessmay occur from the bottoms of the voids 3. However, in accordance withthe construction of FIG. 10, such end-face cracks can be effectivelyprevented from traversing the active layer 13 below the ridge stripe. Ifan end-face crack traverses the active layer, there occur problems inthat the threshold current may increase and the laser beam shape (farfield pattern) may be disturbed. However, adopting the construction ofFIG. 10 will solve such problems. Since the depth of the active layer 13is about 0.6 μm from the crystal surface, it can be easy ensured thatthe bottoms of the voids 3 are located below the active layer 13.

Also in a semiconductor laser device shown in FIG. 11, the voids 3 areformed at positions which are deeper than the position of the activelayer 13. A difference from the construction of FIG. 10 is that bothsides of the optical waveguide region (light-emitting region) 18 areetched deep, and the voids 3 are formed at positions which are below theactive layer 13. In accordance with the construction of FIG. 11,end-face cracks beginning from the voids 3 will never traverse theactive layer 13. In this case, the voids 3 may be formed so as to beshallow.

In a semiconductor laser device shown in FIG. 12, trenches (isolationgrooves) are formed between the voids 3 and the optical waveguide region(light-emitting region) 18. In accordance with the construction of FIG.12, progress of end-face cracks beginning from the voids 3 will beinterrupted by the trenches 35. Moreover, if the trenches 35 are formedwith a depth that traverses the active layer 13, end-face cracks causedby the trenches 35 will not traverse the active layer 13 either. Itsuffices if such trenches 35 are formed only between the voids 3 and theoptical waveguide region (light-emitting region) 18, but each suchtrench 35 may also be formed across the entire region shown by brokenlines in FIG. 12. Trenches can be formed more suitably by a dry etchingtechnique which provides a high level of anisotropy.

The constructions shown in FIGS. 10 to 12 exhibit particular effects inthe case where the chip width is reduced. In future, there will be adesire to obtain as large a number of chips from a single wafer aspossible. In such cases, it will be preferable to reduce the chip widthby adopting the constructions shown.

Embodiment 2

FIG. 13( a) is a plan view showing the neighborhood of an end of thewafer 1 according to the present embodiment. In FIG. 13( a), a pluralityof edge scribings 200 for defining cleavage start positions are shown.The edge scribings 200 are linear grooves which are formed on thesurface of the wafer 1 (peripheral region) by a known instrument such asa scribing tool. The edge scribings 200 are formed at positions wherethe surface of the wafer 1 intersects the cleavage intended planes, andtheir length is set to 0.1 to 1 mm, for example. By applying a physicalforce near such edge scribings 200, cleavage is allowed to begin andprogress.

What is characteristic of the present embodiment is the shape of thevoids 300 in a plane which is parallel to the surface of the wafer 1.FIG. 13( b) is a plan view of the voids 300 in the present embodiment.As is shown in this figure, each void 300 has an anisotropic shape witha longitudinal axis extending along the cleavage direction, both endsbeing pointed. Each void 300 has a length (size along the longitudinalaxis direction) of 5 to 60 μm, for example, and a size along the shorteraxis direction (width and depth) of 3 μm, for example.

With such voids 300, if a cleavage direction deviates between adjoiningvoids 300 from an intended line, the start position of a next-occurringcleavage will be corrected so as to be on the intended line. In the casewhere the width of the voids 300 is set to 3 μm, the deviation of acleavage can be suppressed to 3 μm or less. However, in order to obtainthe effects described with reference to FIGS. 8( a) and (b), it isnecessary to limit the length of the voids 300 along the cleavagedirection; this length is preferably set to 45 μm or less, and morepreferably 20 μm or less.

Note that, since cleavage will progress in one direction (from right toleft in the figure) from the region where the edge scribings 200 areprovided, it is preferable that each void 300 has an “arrow shape” asshown in FIG. 13( c). Each void 300 shown in FIG. 13( b) has “two wings”for receiving a cleavage plane which extends from an adjoining void onthe right side in the figure. These wings have a function of reducingdeviation of cleavage planes. Voids 300 having such a shape may bedifficult to form by the method shown in FIG. 5( b), but can be easilyformed by using a known photolithography and etching technique.

FIG. 14( a) is a plan view showing an example where the voids 300 arearranged with a relatively high density as compared to the example shownin FIG. 13( a). The voids 300 may all be of the same size, but as shownin FIG. 14( b), for example, a structural unit may be constituted by aplurality of voids 300 a, 300 b, and 300 c of different shapes and/orsizes. The voids 300 a, 300 b, and 300 c shown in FIG. 14( b) each have“two wings” for receiving a cleavage plane extending from an adjoiningvoid. Thus, by arranging the plurality of voids 300 a, 300 b, and 300 chaving different sizes of wings as shown in FIG. 14( b) in the order oftheir wing size, it becomes possible to allow the positions of thecleavage planes, which begin to extend from the edge scribings 200, tobe guided onto the intended lines with a high accuracy.

There is a tendency that a deviation of a cleavage plane increases asthe interval between adjoining voids 300 increases. Therefore, it ispreferable to adjust the sizes of wings depending on the intervalbetween adjoining voids 300 or the arraying pitch of the voids 300.Although voids 300 a, 300 b, and 300 c with different sizes of wings arearranged in FIG. 15( b), it is also possible to use only one type ofvoids (e.g., voids 300 c with relatively large wings) for a single wafer1.

It is preferable that those voids 300 which are provided at positionsclosest to the edge scribings 200 have relatively large wings ascompared to the voids which are formed in the other regions. In theexample shown in FIG. 15( a), voids 300 a as shown in FIG. 15( b) arearranged in a large part of the wafer 1, whereas voids 300 c as shown inFIG. 15( c) are disposed at positions closest to the edge scribings 200.

Note that it is also possible to provide the voids 300 a, 300 b, and 300c shown in FIG. 14( b), in this order, only in the region near the edgescribings 200.

INDUSTRIAL APPLICABILITY

As lasers for short-wavelength light sources employing GaN substrateswhich are difficult to be cleaved, mass production of nitride compoundsemiconductor lasers according to the present invention is expected.

1. A nitride compound semiconductor element comprising a substratehaving an upper face and a lower face and a multilayer structuresupported by the upper face of the substrate, such that the substrateand the multilayer structure have at least two cleavage planes, wherein,the multilayer structure includes at least one void which is in contactwith either of the two cleavage planes, and a cross section of the voidin a plane which is parallel to the upper face of the substrate is sizedand shaped so as to be accommodated within a rectangular region of 10μm×10 μm.
 2. The nitride compound semiconductor element of claim 1,wherein the upper face of the substrate has a rectangular shape, and thevoid is located at at least one of four corners of the upper face of thesubstrate.
 3. The nitride compound semiconductor element of claim 1,wherein the multilayer structure has a laser resonator structureincluding: an n-type nitride compound semiconductor layer and a p-typenitride compound semiconductor layer; and an active layer interposedbetween the n-type nitride compound semiconductor layer and the p-typenitride compound semiconductor layer, at least a portion of the cleavageplanes functioning as a resonator end face.
 4. The nitride compoundsemiconductor element of claim 3, wherein an interval between a bottomof the void and the substrate is smaller than an interval between theactive layer and the substrate.
 5. The nitride compound semiconductorelement of claim 3, wherein a trench is formed between a laser opticalwaveguide portion and the void in the multilayer structure.
 6. Thenitride compound semiconductor element of claim 5, wherein an intervalbetween the bottom of the trench and the substrate is smaller than aninterval between the active layer and the substrate.
 7. The nitridecompound semiconductor element of claim 1, wherein the substrate is anitride compound semiconductor.
 8. The nitride compound semiconductorelement of claim 7, comprising a rear electrode formed on the lower faceof the substrate, wherein, the rear electrode has a planar pattern whichallows the void to be visually recognized through the lower face of thesubstrate.